Work to remove spent nuclear fuel from the reactor 4 storage pool at the Fukushima No. 1 complex will begin Tuesday at the earliest, a source close to operator Tokyo Electric Power Co. said Saturday.

Fuel extraction operations started last Monday, with workers first removing 22 unused fuel assemblies that are relatively easier to handle than spent fuel.

Next up is a batch of 22 spent fuel rod assemblies as part of a yearlong effort to remove over 1,000 assemblies from the spent fuel pool of unit 4, a task seen as one of the major hazards in the early stages of dismantling Fukushima No. 1.

It is the first time Tepco is attempting to retrieve fuel assemblies from the reactor 4 pool since reactors 1 to 3 at the plant suffered core meltdowns in March 2011.

Unit 4 was badly damaged by a hydrogen explosion but avoided a meltdown because all of its fuel was in the spent fuel pool while the reactor underwent periodic maintenance work.